1. Field of the Invention
The present invention relates to a holding apparatus for dip coating apparatus which is used to seal an opening of a hollow cylindrical body used as photoreceptor in an electrophotographic copying machine, for example, and to hold the hollow cylindrical body during dipping and coating of an outer surface of the hollow cylindrical body.
2. Discussion of the Related Art
Conventionally, a dip coating method has been considered desirable in coating the outer surface of a hollow cylindrical body or the like, and especially in the case where the smoothness of the film coating is thought to be important. For example, a dip coating method is often employed to form a photoconductive layer on the hollow cylindrical body utilized as a photoreceptor in an electrophotographic copying machine.
In the conventional dip coating method, a hollow cylindrical body is first dipped into the coating solution and is then pulled up at a selected speed. If the hollow cylindrical body is open at its upper and lower ends, the coating solution enters inside the hollow cylindrical body. The inner surface of the hollow cylindrical body is also coated by the coating solution, which will waste the coating solution, and also may cause pollution in the copying machine and difficulty in drying the inner surface of the hollow cylindrical body.
So far various devices have been suggested in order to solve the aforementioned problems. For example, one apparatus blocks the inside of the hollow cylindrical body by using an expanding and contracting air tight bag is disclosed by Japanese Patent Application Unexamined Publication No. Sho. 59-4466. Further, Japanese Patent Application Unexamined Publication No. Sho. 62-241578 provides an apparatus for holding and sealing the upper end of the hollow cylindrical body by pressing a flexible O ring.
An apparatus having a holding member to hold a hollow cylindrical body by frictional contact with its inner surface as it is pulled up by a lifting member is disclosed by Japanese Patent Application Unexamined Publication No. Sho. 63-20068. Moreover, Japanese Patent Application Unexamined Publication No. Sho. 63-264166 shows an apparatus for sealing and holding the upper end of the hollow cylindrical body by pressing various forms of elastic bodies.
However, the above-mentioned proposed devices so far are unsatisfactory. The apparatus disclosed in Japanese Patent Application Unexamined Publication No. Sho. 59-4466 has a problem that a rubber film is liable to be damaged by fatigue due to expansion and contract of the rubber film by pressurized air, and it is difficult to control expansion while many other devices are also being operated simultaneously. The problems with the apparatus disclosed by Japanese Patent Application Unexamined Publication No. Sho. 62-241578 are that the upper end of the hollow cylindrical body cannot be completely sealed and held because an inner diameter of the hollow cylindrical body and the O ring have a low degree of freedom and there is difficulty in controlling the attitude of the hollow cylindrical body while it is being held. Further, an outer surface of the O ring is easily worn out, and the O ring must be exchanged whenever the size of the inner diameter of the hollow cylindrical body changes. A solution of these problems is to enlarge the O ring, but in this case, excessive force is needed to press the O ring, and the force may cause deformation of the hollow cylindrical body.
If a sponge-like elastic body is used as the O ring, oil bleeds from the inside of the elastic body and adheres to a holding portion inside of the hollow cylindrical body because of the excessive pressing force; therefore the hollow cylindrical body sometimes does not separate from the elastic body even after pressing is suspended. Moreover, oil bled from the inside of the elastic body deteriorates the coating solution.
In order to solve the above-mentioned problems, Japanese Patent Application Unexamined Publication No. Sho. 63-264166 provides an apparatus, which improves sealing and holding by using relatively large-sized elastic bodies of various forms. However, the apparatus has a complex form and needs a large compression force and a long compression stroke. Moreover, the manufacturing cost is rather high. There are also problems in controlling the attitude of the hollow cylindrical body because it cannot be perfectly controlled if a position of the hollow cylindrical body before being held was shifted from a predetermined position because of pressing an opening portion of the hollow cylindrical body to a fixed flange. Also, it has a low ability for attitude control the hollow cylindrical body is held only by its upper end. Another problem sometimes appears that the elastic body maintains contact with the hollow cylindrical body and cannot separate therefrom because repetition of expansion and contraction of the elastic body causes fatigue that prevents resumption of the original form.
The apparatus disclosed by Japanese Patent Application Unexamined Publication No. Sho. 63-20068 has a problem that entire sealing and holding mechanisms must be exchanged whenever the size of the inner diameter of the hollow cylindrical body changes.